An anti-reflective lens normally is formed with an anti-reflective coating on a plastic ophthalmic lens. Anti-reflective (AR) coatings are applied to the surfaces of ophthalmic lenses and other optical devices to reduce reflection. For ophthalmic lenses in particular, the reduced reflection makes them not only look better, but more importantly work better because they produce less glare by eliminating multiple reflections, which is particularly noticeable when driving at night or working in front of a computer monitor. The decreased glare means that wearers often find their eyes are less tired, particularly at the end of the day. AR coatings also allow more light to pass through the lens, which increases contrast and therefore increases visual acuity.
The art of casting plastic ophthalmic lenses involves introducing a lens-forming material between two molds and then polymerizing the lens-forming material to become a solid. Liquid plastic formulations such as CR39 monomer are injected into a cavity formed by front and rear molds which have been provided with interior polished mold surfaces for the finished surfaces of the lenses. The plastic is cured in the mold, and then the mold is separated to yield a completed ophthalmic lens which meets a selected prescription. The lens is then ground around the edge to fit into the selected frame. Coatings can be applied to the finished lens or to the inside of the front or rear mold, whereupon they will bond to the lens upon curing.
Some optometrists offer on-site eyeglass services. Several companies have developed methods by which lenses can be cast on site, in an office. However, current methods of applying AR coatings to eyeglasses require that they be shipped to a different facility because the AR coatings must be applied via vacuum vapor deposition. This of course means additional time and expense. There is therefore a need for a method for making eyeglasses with an AR coating on-site.
One type of AR coating that is used for ophthalmic lenses is an alternating stack of a high index material and a low index material. The most commonly used low index material is silicon dioxide; zirconium dioxide and/or titanium dioxide is often used as the high index material.
An issue with AR coatings, particularly as applied to plastic ophthalmic lenses, is adhesion. AR coatings are generally applied via vacuum deposition. It is well known that adhesion of vacuum-deposited coatings to their substrates is in general problematic. The organic, plastic lens material and inorganic AR material do not readily adhere to each other, resulting in peeling or scratching. Accordingly, a new method is needed to apply an AR coating to a plastic lens with greater adhesion.
Several patents are understood to disclose using silanes to bind an inorganic matrix to an organic matrix. U.S. Pat. No. 5,733,483 to Soane et al. teaches using a coupling layer to tie together an AR multilayer made of silicon oxide and an acrylate-containing lens. The coupling agent has a siloxy head and an acrylate tail. An example of a silane used therein is methacryloxypropyltrimethoxysilane.
U.S. Pat. No. 4,615,947 to Goosens teaches an acrylic mixed with an organopolysiloxane to increase the adhesion of an organosiloxane hard coat to a thermoplastic substrate. U.S. Pat. No. 5,025,049 to Takarada et al. also teaches a primer for increasing adhesion of an organopolysiloxane layer to a thermoplastic substrate. The primer is a mixture of an organic copolymer including an alkoxysilylated monomer and other ingredients.
Other patents discuss using silanes to bind an organic matrix to another organic matrix. U.S. Pat. No. 6,150,430 to Walters et al. teaches using organofunctional silanes to improve the adherence of an organic polymeric layer to an organic polymeric substrate.
U.S. Pat. No. 5,096,626 to Takamizawa et al. teaches a plastic lens having an AR coating and/or hard coat. The patent discusses poor adhesion of prior art methods and says they achieve excellent adhesion by forming the lens using a set of molds, wherein the AR coating is first applied to one of the molds and then the lens monomer is poured between the molds and polymerized. A silane coupling agent such as methacryloxypropyltrimethoxysilane can be included in the hard coat/AR coat solution, which may contain colloidal silica, colloidal antimony oxide or colloidal titanium dioxide.
U.S. Pat. No. 6,986,857 to Klemm et al. teaches a method of assembling a lens with a top coat, AR coat, scratch resistant coat, impact resistant primer, and lens substrate. Klemm's solution to the issue of poor adherence of the top coat to the AR coat is to apply the first layer of the AR coating (which comprises a stack of four layers) as two sublayers of SiO2. Another thin layer of SiO2 is applied between the AR stack and the scratch resistant coating to improve adherence between the two.
The above references in general use sol gel chemistry and require high heat (≧80° C.). Heating to high temperature, however, is not suitable for casting and curing lenses in plastic molds because the optical surface of the mold will be distorted.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.